Brazil international Coutinho joined the Catalan side from Liverpool in January 2018 in a deal worth an initial £105 million ($142m).
Although Coutinho has made 50 appearances in all competitions this season for Ernesto Valverde's team, he is often used from the bench.
Mane is confident things will get better for his old team-mate at Camp Nou, but he hopes he is kept out of the starting XI once again when Liverpool visit Barcelona for the first leg of their semi-final tie.
"He is a great, great player and I'm a little bit jealous that Barcelona can get him," Mane told reporters ahead of Wednesday's game. "I would love to see him.
"But we are happy for him. He really enjoyed playing alongside his team-mates and gave everything, and is still young and can improve a lot. I know him, he is a hard worker.
"Hopefully he will still be in bed when we play!"
Reds coach Jurgen Klopp admitted he still misses the former Anfield hero who made over 200 appearances for the club, but is happy with the way his team have responded to his departure as their challenge for Premier League and Champions League titles continues.
“I am happy to see Phil again. It’s up to Mr Valverde whether he starts," he said.
"I know a lot of people make shit stories about that. Yes we miss Phil Coutinho a lot because he's a world class player. I loved working together with him but we've had to deal without him and we've done well. That's all I can say about that. He's a really good player."
"When I first heard he wanted to go to Barcelona, I couldn't imagine that we would do this well without him but we did and it's all good."